A typical Area Array Package (AAP) device such as a Ceramic Column Grid Array (CCGA) device or a Ball Grid Array (BGA) device includes a substrate, a die and a heat spreader. The substrate includes layers of non-conductive material and conductive material sandwiched together into a substantially plane-shaped element which supports (i) an array of circuit board contacts on one side (e.g., columns, balls, etc.) for connecting to a circuit board, and (ii) die contacts on the other side for connecting to the die. The die is a silicon-based chip containing integrated circuitry which generates heat during operation. The heat spreader (or lid) typically glues to the side of the substrate having the die contacts (e.g., using a thermal adhesive) and extends over the die to physically protect the die. A thermally conductive but electrically non-conductive material (e.g., thermal grease) resides typically between the heat spreader and the die to convey heat from the die to the heat spreader during operation.
When a circuit board manufacturer assembles a circuit board module having the AAP device, the manufacturer first solders the AAP device to a circuit board so that the heat spreader faces away from the circuit board. The manufacturer then attaches a heat sink to the heat spreader using, for example, metallic clips. During operation of the AAP device, the heat spreader transfers heat from the die to the heat sink. The heat sink then dissipates that heat into the surrounding environment.
It should be understood that the external metallic clips, which hold the heat sink in place, electrically connect both the heat spreader of the AAP device and the heat sink to a ground reference of the circuit board (e.g., ground pads or ground vias disposed around the AAP device) to prevent the heat spreader and the heat sink from operating as an antenna due to capacitive coupling between the die and the heat spreader. Accordingly, during operation of the AAP device, the heat sink, the heat spreader and the external metallic clips operate as an electromagnetic interference (EMI) barrier to block EMI radiating from the die rather than a transmitter which distributes that EMI into the surrounding environment.